if targets are unspecified, builds the 'default' target (see manual).
options: --version print ninja version ("1.9.0") -v, --verbose show all command lines while building
-C DIR change to DIR before doing anything else -f FILE specify input build file [default=build.ninja]
-j N run N jobsin parallel (0 means infinity) [default=10 on this system] -k N keep going until N jobs fail (0 means infinity) [default=1] -l N do not start new jobsif the load average is greater than N -n dry run (don't run commands but act like they succeeded) -d MODE enable debugging (use '-d list' to list modes) -t TOOL run a subtool (use '-t list' to list subtools) terminates toplevel options; further flags are passed to the tool -w FLAG adjust warnings (use '-w list' to list warnings)
简单使用的话，我们关注它的两个参数就行了
-f：这个参数指定的就是输入文件，也就是 makefile 和 bp 转换后的 ninja 文件，一般位于 ./out 目录，后面会说
